Methods for producing polysilicon resistors

ABSTRACT

A method for producing a polysilicon resistor device may include: forming a polysilicon layer; implanting first dopant atoms into at least a portion of the polysilicon layer, wherein the first dopant atoms include deep energy level donors; implanting second dopant atoms into said at least a portion of said polysilicon layer; and annealing said at least a portion of said polysilicon layer.

RELATED APPLICATION(S)

This application is divisional of U.S. patent application Ser. No.14/048,173, entitled “METHODS FOR PRODUCING POLYSILICON RESISTORS”,filed Oct. 8, 2013, the contents of which are incorporated herein byreference.

TECHNICAL FIELD

The disclosure relates to methods for manufacturing polysiliconresistors in semiconductor components, especially for producing precisepolysilicon resistors, e.g. resistance temperature sensors, and forproducing polysilicon resistors having well-controlled temperaturecoefficients.

BACKGROUND

With the introduction of the silicon planar technology, not only theactive components like NMOS transistors (N-typemetal-oxide-semiconductor transistors), PMOS transistors (P-typemetal-oxide-semiconductor transistors) and bipolar transistors, but alsothe passive components like resistors are required to qualify with thesilicon planar technology. The use of polycrystalline silicon, orpolysilicon as it is commonly known, as a resistor, is well known in thefabrication of semiconductor devices. Generally polysilicon resistivityeither increases or decreases with increasing temperature. This rate ofincrease is referred to as a temperature coefficient of resistance. Onone hand, a precise resistor requires not only the property of stabilityand low-scattering, but also a relative high sheet resistance to keepthe resistor as small as possible. For high-ohm resistors, which can besimply achieved by series connection of square sheets with sheetresistance of 1 kOhm/square, and the typical minimum critical dimensionof such square sheet is in a range of 0.5 μm-1 μm (for example, a 500kOhm resistor would be built up from 500 pieces of such square sheets),the resistance value of such high-ohm poly resistors produced in aconventional way varies too much with regard to the temperature, i.e.the temperature coefficient of the high-ohm poly resistors is too big,which results instability of the poly resistors. For these reasons,there is a need for minimizing the temperature dependence of apolysilicon resistor.

On the other hand, polysilicon resistors are utilized for a variety ofapplications, e.g. used as temperature sensors in semiconductor devices.Power transistors such as DMOS transistors (double diffused metal oxidesemiconductor transistors) find multiple applications in semiconductorapplications. During operation of the power transistors, a wide varietyof switching states occur, in which in part very large power losses areconverted into heat. Such switching states associated with large powerlosses are critical since the temperature rises greatly in this case andthe power transistors can be destroyed by overheating. In order toprotect the transistors against damage in such critical switchingstates, temperature sensors are often used. Ideally, the temperaturesensors are positioned as close as possible to or in the cell array ofthe power transistor in order that a temperature rise on account ofenergy loss converted into heat is detected early and rapidly and thatthe power transistor is turned off in good time before self-destructionon account of overheating by an auxiliary circuit such as a logiccircuit. In this case, a resistor situated in the cell array of thepower transistor can be used as a rapidly reacting temperature sensor.The temperature sensor changes its absolute resistance value withtemperature in the characteristic manner, in which case it is possibleto derive a turn-off signal for turning off the power transistor when adefined maximum permissible resistance value is reached. Therefore, anobvious variation of resistance according to temperature increasing isrequired for such polysilicon resistance temperature sensors. For thesereasons, there is a need for enlarging the temperature dependence of apolysilicon resistance temperature sensor in certain applications.However, this concept with a resistance temperature sensor often failsin practice because of excessively large manufacturing variations withwhich a resistance temperature sensor of this type can be produced,since the absolute value of the resistance cannot be used as a turn-offthreshold meaningfully. For these reasons, there is a need forminimizing the manufacturing-variations dependence of such polysiliconresistance temperature sensor.

Thus, there is a need in the art to provide methods for manufacturingpoly resistors precisely and in the meantime, for manufacturing polyresistors with well-controlled temperature coefficients.

BRIEF SUMMARY

In accordance with one or more embodiments, a method for producing apolysilicon resistor device may include: forming a polysilicon layer;implanting first dopant atoms into at least a portion of saidpolysilicon layer, wherein the first dopant atoms comprise deep energylevel donors; implanting second dopant atoms into said at least aportion of said polysilicon layer; and annealing said at least a portionof said polysilicon layer after implanting the first and second dopantatoms.

In accordance with one or more embodiments, a method for producing apolysilicon resistor device may include: forming a polysilicon layer;forming an implantation mask over said polysilicon layer exposing apre-defined subarea of said polysilicon layer; implanting dopant atomsinto said pre-defined subarea of said polysilicon layer through saidimplantation mask; and creating diffusion of said dopant atoms, whereinsaid dopant atoms diffuse at most within said polysilicon layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIG. 1 is a graphical representation of the temperature behavior of ahigh-ohm poly resistor produced according to a conventional method.

FIG. 2A is a flow diagram illustrating a method of fabricating apolysilicon resistor device in accordance with an aspect of the presentdisclosure.

FIG. 2B is a flow diagram illustrating a method of fabricating a lowtemperature coefficient polysilicon resistor in accordance with anaspect of the present disclosure.

FIG. 3A shows a grain structure of crystallized polysilicon.

FIG. 3B shows a grain structure of amorphized polysilicon.

FIG. 4 is a graphical representation of the temperature behavior of polyresistors produced in accordance with some aspects of the presentdisclosure.

FIG. 5 is a sectional and perspective view of a polysilicon resistancetemperature sensor produced according to an aspect of the presentdisclosure.

FIG. 6 is a cross-section view of a polysilicon resistance temperaturesensor with manufacturing fluctuation in a prior art.

FIG. 7A is a flow diagram illustrating a method of fabricating apolysilicon resistor device in accordance with an aspect of the presentdisclosure.

FIG. 7B is a flow diagram illustrating a method of fabricating a precisepolysilicon resistance temperature sensor in accordance with an aspectof the present disclosure

FIG. 8A depicts the polysilicon resistance temperature sensor afterformation of a polysilicon layer in accordance with an aspect of thepresent disclosure.

FIG. 8B depicts the polysilicon resistance temperature sensor afterformation of a implantation mask in accordance with an aspect of thepresent disclosure.

FIG. 8C depicts the polysilicon resistance temperature sensor afterdoping and diffusion in accordance with an aspect of the presentdisclosure.

FIG. 9A depicts the polysilicon resistance temperature sensor afterformation of a polysilicon layer in accordance with an aspect of thepresent disclosure.

FIG. 9B depicts the polysilicon resistance temperature sensor afterformation of an implantation mask in accordance with an aspect of thepresent disclosure.

FIG. 9C depicts the polysilicon resistance temperature sensor afterdoping and diffusion in accordance with an aspect of the presentdisclosure.

FIG. 10A depicts the polysilicon resistance temperature sensor afterformation of a polysilicon layer in accordance with an aspect of thepresent disclosure.

FIG. 10B depicts the polysilicon resistance temperature sensor afterformation of an implantation mask in accordance with an aspect of thepresent disclosure.

FIG. 10C depicts the polysilicon resistance temperature sensor afterdoping and diffusion in accordance with an aspect of the presentdisclosure.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the disclosure maybe practiced. In this regard, directional terminology, such as “front,”“back,” “leading,” etc., is used with reference to the orientation ofthe figures being described. Because components of embodiments can bepositioned in a number of different orientations, the directionalterminology is used for purposes of illustration and is in no waylimiting. It is to be understood that other embodiments may be utilizedand structural or logical changes may be made without departing from thescope of the present disclosure. The following detailed description,therefore, is not to be taken in a limiting sense, and the scope of thepresent disclosure is defined by the appended claims.

It is to be understood that the features of the various exemplaryembodiments described herein may be combined with each other, unlessspecifically noted otherwise.

Polysilicon resistor device fabrication involves performing a variety ofprocesses, procedures and operations in order to achieve a fabricateddevice. These operations include, but are not limited to, layering,doping, heat treatments, and patterning.

Layering is the operation used to add layers of a selected thickness toa wafer substrate. These layers can be insulators, semiconductors,conductors, and the like and can be grown or deposited by a number ofsuitable methods (e.g., chemical vapor deposition, sputtering, and thelike). Doping is the process that introduces specific amounts of dopantsin the wafer surface through openings in the surface layers. Typicaltechnique used for doping is, e.g. ion implantation. Doping is used, forexample, to create active regions in transistors or to createdresistivity regions in resistors. Heat treatments are operations inwhich a complete wafer or a portion of a wafer is heated and hold at apredefined temperature (range) for some pre-determined time to achievespecific results. A common heat treatment is called an annealing whichis typically employed to repair defects in crystal structures introducedby ion implantation. Patterning is the operation that employs a seriesof steps that result in the removal of selected portions of addedsurface layers. The series of steps includes first forming a layer ofresist or photoresist over a polysilicon resistor device. Then a resistmask is aligned with the device. Subsequently, the layer of resist isexposed or irradiated through the resist mask, which selects portions oflayer of resist that are later removed to expose underlying portions ofthe device. Continuing, a fabrication process, such as ion implantation,ion diffusion, and the like is performed on exposed portions of thedevice.

For example, the prevalent processes for producing a high-ohmpolysilicon resistor in the market nowadays typically include:depositing an undoped polysilicon layer over an insulating layer of asilicon substrate, the undoped polysilicon layer is typically in athickness range of 200 nm to 400 nm; then implanting dopant atoms intothe polysilicon layer with a subsequent annealing step, which definesthe resistance of the polysilicon resistor.

Generally, polysilicon resistivity either increases or decreases withincreasing temperature. This rate of increase is referred to as atemperature coefficient of resistance. FIG. 1 illustrates thetemperature behavior of a high-ohm resistor produced according to thegeneral process mentioned above. The high-ohm poly resistor has aresistance value of 1 kOhm at room temperature (27° C.), and theresistance value decreases significantly as the working temperatureincreases, i.e. the high-ohm poly resistor has a negative temperaturecoefficient, however the temperature coefficients has a large absolutevalue which is not appropriate for a resistor device in someapplications.

The following embodiments provide methods for improving the temperaturebehavior of polysilicon resistors, more specifically, for stabilizingthe temperature behavior of the resistance.

According to an aspect of one or more embodiments described in thefollowing, first dopant atoms including deep energy level donors may beimplanted into at least a portion of a polysilicon layer. In one or moreembodiments, implanting the first dopant atoms may at least partiallyamorphize the at least a portion of the polysilicon layer. The deepenergy level donors (also referred as deep level donors or deep energydonors) implanted into the polysilicon layer may inhibit a fullrecrystallization of said at least a portion of the polysilicon layerduring a later annealing process. In one or more embodiments, an energydifference between the deep energy donors and the conduction band edge(e.g., an energy difference between an energy level of the deep energydonors (e.g. an energy level of the band structure of the dopedpolysilicon layer provided by the deep energy donors) and an energylevel of the conduction band edge (e.g. an energy level of theconduction band edge in the doped polysilicon layer, e.g. an energylevel of the lower edge of the conduction band in the band structure ofthe doped polysilicon layer) may be higher than 200 meV. In one or moreembodiments, such deep energy donors can be selenium atoms, sulfur atomsor nitrogen atoms.

According to another aspect of one or more embodiments described in thefollowing, second dopant atoms may be implanted into said at least aportion of the polysilicon layer. In one or more embodiments, the seconddopant atoms can be different dopant atoms than the first dopant atoms.In one or more embodiments, the second dopant atoms may be dopant atomswith a shallow energy level (also referred as shallow donors). Suchshallow donors may exhibit a small difference between an energy level ofthe doping atoms and the conduction band edge; for example, a differencesmaller than 100 meV according to one or more embodiments. In one ormore embodiments, the second dopant atoms may include or may bephosphorous atoms or arsenic atoms.

In one or more embodiments, implanting the second dopant atoms may becarried out after implanting the first dopant atoms. In one or moreembodiments, implanting the second dopant atoms may be carried outbefore implanting the first dopant atoms. In one or more embodiments,implanting the first dopant atoms and implanting the second dopant atomsmay be carried out at the same time.

In accordance with various embodiments, an annealing process may becarried out after the first and second dopant atoms have been implantedinto the polysilicon layer.

FIG. 2A is a flow diagram illustrating a method 200 a of fabricating apolysilicon resistor device in accordance with an aspect of the presentdisclosure. The method 200 a includes forming a polysilicon layer (in202 a); implanting first dopant atoms into at least a portion of thepolysilicon layer (in 204 a), wherein the first dopant atoms includedeep energy level donors; implanting second dopant atoms into the atleast a portion of said polysilicon layer (in 206 a); and (in 208 a)annealing the at least a portion of said polysilicon layer afterimplanting the first and second dopant atoms.

FIG. 2B is a flow diagram illustrating a method 200 b of forming apolysilicon resistor with relatively smaller temperature coefficients inaccordance with an aspect of the present disclosure. The method 200 bpre-implants deep energy level donors into the polysilicon resistorbefore optionally additionally any of the typical or customary dopingimplantation is performed. The pre-implantation changes the crystalstructure of the polysilicon, rendering it amorphous or at leaststrongly damaged depending upon the energy of implantation. Thepre-implanted atoms affect the recrystallization characteristics of thepolysilicon during annealing, resulting for example in a partialrecrystallization of the amorphized structure, with the result that thetemperature behavior of the polysilicon can be selectively altered. Moreparticularly, as shown, method 200 b results in a stabilized temperaturebehavior of the polysilicon resistor.

The method 200 b begins at block 202 b, wherein a semiconductordevice/body is provided. The semiconductor device can have otherdevices, including DMOS transistor devices, capacitors, and the likethat are partially fabricated. An oxide layer is formed over the deviceat block 204 b. The oxide layer serves to protect underlying layers,which can include active components, semiconductor substrate, and thelike. A polysilicon layer is deposited over the oxide layer at block 206b and has a selected thickness. Typically, the thickness of apolysilicon layer is in a range of between 200 nm-400 nm. Thepolysilicon layer can be formed as undoped or lightly-doped byincorporating a dopant during deposition.

Optionally, an implantation mask is applied to the semiconductor devicethat exposes a selected portion and/or percentage of the polysiliconlayer while covering other portions of the polysilicon layer (not shownin FIG. 2B), so that only the exposed region of the polysilicon layer isimplanted subsequently. The amount or percentage of the polysiliconexposed by the implantation mask is determined based on a desired dopantconcentration, the selected thickness of the polysilicon layer, anddopant species and dose employed in later implantation.

Continuing the method 200 b at block 208 b, deep energy level donors arepre-implanted into the exposed portions of the polysilicon layer, sothat polymer behavior of the polysilicon is optimized. Morespecifically, the grain structure of the polysilicon is amorphized or atleast partially amorphized via pre-implanting deep energy donors. Thedeep energy atoms are selected from substances that can create deeplevel defects. Particularly suitable deep energy level donors comprise,e.g. selenium atoms, nitrogen atoms or sulfur atoms; such deep energylevel defects result in an effective doping concentration increasingwith temperature and a significant reduced Schottky resistance. Typicalpre-implantation dose lies in a range of between 1×10¹⁵ cm⁻² and 5×10¹⁵cm⁻². FIG. 3A shows an example of the original crystalline grainstructure of polysilicon, while FIG. 3B illustrates the grain structureof polysilicon been amorphized.

Optionally, pre-implantation includes pre-implanting second dopant atomsadditionally (not shown in FIG. 2B). The second dopant atoms aretypically selected from e.g., phosphorus atoms.

Then, any actual doping (where such doping would typically take place)may be performed through the exposed portions of the poly resistor withsecond dopant atoms at block 210 b. The second dopant atoms contributeto the resistivity/conductivity of the polysilicon resistor. The seconddopant atoms employed in the implant are typically phosphorous atoms,with a typical implantation dose in the range of between 3×10¹⁴ cm⁻² and4×10¹⁴ cm⁻², and implantation energy of 40 keV.

Optionally, metal contacts are formed at ends of the polysiliconresistor (not shown in FIG. 2B). The contacts are formed of a conductivematerial, such as aluminum, tungsten or copper, and provide electricalcommunication to other electronic components. In one embodiment, the endregion of the polysilicon resistor, where the contacts are positioned,is highly-doped compared to the central region of the poly resistor,thereby to have relatively little electrical resistance. A typicalphosphorous implantation energy of 40 keV with implantation dose of2.7×10¹⁵ cm⁻² are applied to the contact region of the poly resistor.Then, the implantation mask (e.g. resist mask) is removed by a suitableprocess, e.g. a suitable resist removal process.

Subsequently, a thermal activation process comprising an annealing isperformed at block 212 b that activates and diffuses dopants implantedwithin the polysilicon resistor. As the implanted nitrogen highlyeffects the crystalline structure of the polysilicon and results in ahighly disordered crystal structure, rendering the subsequent annealingprocess capable of recrystallizing the amorphized region partially, soas to control the conductivity/resistivity of the resistor to a requiredlevel. Subsequently, fabrication of the polysilicon resistor and thedevice continues with other processes including, but not limited to,contact formation.

Graphical representations of the temperature behavior of high-ohm polyresistors produced according to the above methods are illustrated inFIG. 4, wherein curve 402 represents a temperature behavior of ahigh-ohm poly resistor produced in a conventional method, morespecifically, the high-ohm poly resistor is produced merely with actualdoping step, with a phosphorous implantation dose of 8.7×10¹⁴ cm⁻²;curve 404 represents a temperature behavior of a high-ohm poly resistorproduced according to one aspect of the current disclosure, morespecifically, with pre-implantation of nitrogen in a dose of 5×10¹⁵ cm⁻²and doping of phosphorous in a dose of 3×10¹⁴ cm⁻²; curve 406 representsa temperature behavior of a high-ohm poly resistor produced according toone aspect of the current disclosure, more specifically, withpre-implantation of nitrogen in a dose of 5×10¹⁵ cm⁻² and doping ofphosphorous in a dose of 4×10¹⁴ cm⁻²; and curve 408 is a mixedcalculation result of the temperature behavior showed as curve 404 andcurve 406. As illustrated in FIG. 4, over the same temperature range(from −40° C. to +120° C.), the resistance value of the poly resistorsproduced with pre-implantation of deep energy donors (curves 404, 406and 408) is more stable compared to the poly resistor produced withoutpre-implantation (curve 402), and the temperature coefficients of thepoly resistors produced with pre-implantation are almost only half asthe temperature coefficient of the poly resistor produced withoutpre-implantation.

In one implementation of the present disclosure, the method is appliedin a polysilicon layer having a thickness of 200 nm. With apre-implantation energy of 50 keV and a nitrogen dose of 5×10¹⁵ cm⁻²,the entire polysilicon layer is amorphized.

In some embodiments, in order to stabilize the temperature coefficientsof high-ohm poly resistors, undoped polysilicon is pre-amorphized usingnitrogen pre-implantation, and the high proportion of nitrogen in thepolysilicon inhibits the grain growth during subsequent annealing. Whilethe pre-amorphization and subsequent annealing yield their intendedeffects of a reduced carrier mobility by an enhanced scattering atlattice defects, the temperature coefficients of the poly resistor maythus be independently or partially independently controlled, which canlead to a resistor with more stable temperature responses.

One typical implementation of the present disclosure for producing apoly resistor is presented below: first, a polysilicon layer with arequired thickness, e.g. 200 nm-400 nm, is deposited in, e.g. a LPCVD(Low Pressure Chemical Vapor Deposition) furnace; then pre-implantationof nitrogen atoms is carried out for amorphizing the polysilicon, withan implantation dose of 5×10¹⁵ cm⁻² and an implantation energy of 50keV; subsequently, the actual or typical doping with phosphorous atomsis performed for setting the sheet resistance of the polysilicon to 1kOhm/square, and the implantation energy is set to 40 keV with animplantation dose of 3.5×10¹⁴ cm⁻²; further, the end region of thepolysilicon layer where the contacts are formed is high-doped withphosphorous atoms to have a rather little electrical resistance, and theimplantation energy is set to 40 keV with an implantation dose of2.7×10¹⁵ cm⁻²; optionally, the polysilicon layer is cut into requiredshape by e.g. lithography; at last, an annealing is performed topartially activate the conductivity dopants in the polysilicon layer,since the high percentage of pre-implanted nitrogen inhibits therecrystallization of the grain structure resulting in a temperaturestable reduced mobility of free charge carriers.

In some embodiments, deep defects are created in order to reduce theSchottky barrier created in the polysilicon-metal contact region, so asa more reliable ohmic contact can be formed. To form such ohmic contact(or low resistance exhibiting ohmic properties), the Schottky barrierheight should be small everywhere. Creation of deep energy level defectscan reduce the Schottky barrier, wherein the deep defects can be formedby pre-implantation of deep energy level donors, e.g. selenium into thecontact region.

The following embodiments provide methods for improving the temperaturebehavior of polysilicon resistors, more specifically, for improving thetemperature behavior of the resistance.

It is well known in the prior art using polysilicon resistors astemperature sensors in semiconductor devices. Conventionally,polysilicon resistance temperature sensors are positioned as close aspossible to or in the cell array of a power transistor in order todetect the temperature rising early and rapidly. The absolute resistancevalue of a polysilicon resistor is determined by the dopants implantedinto the resistor and subsequent annealing. It is noted that the dopantsimplanted into the resistor normally do not entirely contribute to theresistance of polysilicon resistor, since the dopants may diffuse intothe other layers beneath/above the polysilicon layer, and their mobilitymay be reduced in the surface and boundary regions. In some embodiments,the polysilicon resistance temperature sensor is produced in a stripeshape as illustrated in FIG. 5. The longitudinal direction of the stripelies in y-axis, the width of the cross section of the strip lies inx-axis, and the depth of the cross section of the strip lies in z-axis.While the dopants fulfill the polysilicon stripe, the dopants whichactually contribute to the conductivity of the resistor may fluctuateamong a plurality of polysilicon stripes, even with the sameimplantation and annealing setting, since the surface/boundary of thepoly stripes may have size fluctuations due to the manufacturingimprecision. In other word, the absolute resistance value of apolysilicon resistor varies with the fluctuation of the resistor′structure and doping. For example, as illustrated in FIG. 6, in theconventional manufacturing procedure, typical width fluctuation of apolysilicon resistor stripe with a thickness of about 1 μm is ±500 nm(shown as double-arrow 602 in FIG. 6), the fluctuation of the thicknessof the poly resistor is about ±10% (shown as double-arrow 604 in FIG.6), while the self-doping can be adjusted accurately to about ±8%relative to the dose (shown as 606 in FIG. 6). For a plurality of polyresistor applications, the fluctuation of the poly width and thicknessintroduced by the manufacture would therefore be negligible. However,much of the space on the chip may be lost due to the fluctuation of thepoly resistor width (typical width of a poly resistor lies in the rangesof 30 μm-100 μm). Further, the conventional methods would fail toproduce high accuracy poly resistors, e.g. a polysilicon resistancetemperature sensor with the fluctuation of the resistance value lieswithin ±5%.

One or more embodiments provide methods of manufacturing polysiliconresistance temperature sensors, with more accurate resistance.

According to an aspect of one or more embodiments described in thefollowing, dopant atoms may be implanted through an implantation maskinto a pre-defined subarea of a polysilicon layer. Subsequently,diffusion of said dopant atoms may be created (for example, by annealingat least the subarea of the polysilicon layer), wherein said dopantatoms diffuse at most within said polysilicon layer. In one or moreembodiments, the dopant atoms may diffuse at most within a portion ofthe polysilicon layer. For example, in one or more embodiments, thediffusing dopant atoms may not reach a boundary of the polysiliconlayer.

FIG. 7A is a flow diagram illustrating a method 700 a of fabricating apolysilicon resistor device in accordance with an aspect of the presentdisclosure. The method 700 a includes: forming a polysilicon layer (in702 a); forming an implantation mask over the polysilicon layer exposinga pre-defined subarea of the polysilicon layer (in 704 a); implantingdopant atoms into the pre-defined subarea of the polysilicon layerthrough the implantation mask (in 706 a); and creating diffusion of thedopant atoms, wherein the dopant atoms diffuse at most within thepolysilicon layer (in 708 a).

FIG. 7B is a flow diagram illustrating a method 700 b of fabricating apolysilicon resistance temperature sensor in accordance with an aspectof the present disclosure. Generally, the absolute resistance value ofpolysilicon resistor varies as a result of manufacturing variations,such as in the cross-sectional profile of the polysilicon structure. Themethod 700 b mitigates this affect by polysilicon masking and doping asubset of the polysilicon, creating a sensor in a controlled volume,such as in the central region of the polysilicon.

Beginning at block 702 b, a semiconductor device/body is provided. Thesemiconductor device can have other devices, including DMOS powertransistors, capacitors, and the like that are partially fabricated. Anoxide layer that may be formed over the device at block 704 b serves toprotect underlying layers, which can include active components,semiconductor substrate, and the like and also to electrically isolatethe polysilicon resistor. A polysilicon stripe may be formed on theoxide layer at block 706 b having a selected thickness. The polysiliconstripe may be formed as undoped polysilicon. The thickness of thepolysilicon stripe is typically selected according to other components,such as polysilicon gate layers, formed on the device. An implantationmask (e.g., resist mask) applied to the semiconductor device at block708 may be configured to expose a selected portion and/or percentage ofthe polysilicon resistor in the central region while covering otherportions of the resistor and other components on the device, so thatonly the exposed region of the polysilicon is implanted by subsequentprocesses. The amount or percentage of the polysilicon exposed by theimplantation mask (e.g. resist mask) may be determined based on adesired dopant concentration, a selected thickness of the polysiliconstripe, and dopant species and dose employed in later ion implantation,so that the dopants implanted subsequently will not diffuse out of thestripe. A selected type dopant is then implanted into the exposedportions of the polysilicon stripe at block 710 b. Since ionimplantation can be set with a very good accuracy (typically ±2%)regarding to the implantation dose, thus the doping concentration intothe poly stripe is possible to be set very precisely. Subsequently, theimplantation mask (e.g., resist mask) may be removed. A thermalactivation process is performed at block 712 b that activates anddiffuses dopants implanted within the polysilicon stripe. The thermaltreatment may include an annealing process which is able to activate theimplanted dopants almost 100% electrically.

With this provided method, the dopants are only introduced in thecentral region of the polysilicon stripe, and will not suffer fromsurface/boundary effects. Therefore, these dopants completely contributeto the resistivity of the polysilicon resistance temperature sensors.Since the fluctuation of resist mask size can be controlled within1%-2%, and ion implantation dose has an error range about 2%-3%,consequently, a total variation of less than 5% regarding to theresistance value can be achieved.

FIGS. 8A, 8B and 8C depict a polysilicon resistor device 800 beingfabricated according to one aspect of the current disclosure. The device800 as shown is provided and described to facilitate understanding ofthe present disclosure and is exemplary in nature.

FIG. 8A depicts the polysilicon temperature sensor after formation of apolysilicon stripe 806 in accordance with an aspect of the presentdisclosure. The polysilicon stripe 806 may be formed on an oxide layer804 by a suitable deposition process, while the oxide layer 804 is shownover a semiconductor substrate or body 802 comprised of silicon. Thethickness 850 of the deposited polysilicon stripe 806 may be chosen tobe large enough, so that the oxide layer 804 cannot be reached by thesubsequent diffusion of the dopant in further steps, and thus the oxidelayer 804 is segregated from the dopants.

FIG. 8B illustrates the polysilicon resistor device 800 after formationof mask 808 exposing a central portion of the polysilicon stripe 806 inaccordance with an aspect of the present disclosure. The resist mask 808has an opening 810. The opening 810 is typically uniformly spaced alongthe polysilicon stripe 806 so as to facilitate uniform dopantdistribution of implanted dopants in the longitudinal direction(y-direction) of the poly resistor 806. The width 860 of the opening 810can be varied. In one embodiment, the width 860 is set to size X₁ tomake sure the lateral diffusion range 864 of the subsequent implantedspecies in the lateral direction (x-direction) is within the regionbetween two side flanks 812 and 814 of the poly stripe 806, or even hasa significant distance away from the flanks. Then the fluctuation of thestripe width and thickness are eliminated for determining the absoluteresistance value of the poly stripe, and the width 860 of mask opening810 is now the critical dimension of the poly resistor, while themasking technology has merely a 1%-2% error range impact.

FIG. 8C illustrates the polysilicon temperature sensor 800 after ionimplantation 816 in accordance with an aspect of the present disclosure.The dopants can merely pass through the opening 810, but are resisted inother portions by the resist mask 808. As a result, only a portion ofthe ions directed at the opening 810 are implanted into the polysiliconresistor, forming an implanted region 806 a. Subsequent to the ionimplantation 816, the resist mask 808 is removed by a suitable process(e.g., chemical solution). Then, a thermal activation process isperformed that diffuses the implanted dopants more uniformly through thepolysilicon stripe 806, forming a diffused region 806 b.

Accordingly, the poly stripe 806 is shown composed of an implantedregion 806 a, a diffused region 806 b and an undoped region 806 c. Theabsolute resistance value of the poly stripe 806 is merely determined bythe masking 808 (or the opening 810), and doping dose and energy, andthe influence from the fluctuation of the structure of poly stripe 806to the absolute resistance value is eliminated. Further, since thethickness and lateral size of the poly stripe 806 are significantlylarger than the diffusion scope of the implanted dopant, no dopant candiffuse away from the poly stripe 806, reducing or eliminating dopantthat may become electrically inactive due to surface/boundary effects(e.g. space charge zone, the interstitial space, etc.), and such thatfewer or no charge carriers may suffer a decreased mobility due tosurface roughness of the stripe 806. Therefore, with the above exemplaryembodiment, the size and shape of the poly stripe may now be independentof the resistance value. Stated another way, the effective cross-sectionof the device may be limited to a subset of the gross stripecross-section, with the result that the profile of the deposited stripedoes not define the resistance value of poly stripe any more, whereasthe now undoped region 806 c would have led to potentially undefinedconditions and unwanted process variations, or variations that present agreater practical challenge to control.

FIGS. 9A, 9B and 9C depict a polysilicon resistance temperature sensor900 being fabricated according to one aspect of the present disclosure.The device 900 provided in FIG. 9 is different from the device 800illustrated in FIG. 8 in the polysilicon stripe thickness, and leads toa reduction of undefined and unwanted region in the poly stripe.

FIG. 9A depicts the polysilicon resistance temperature sensor afterformation of a polysilicon stripe 906 in accordance with an aspect ofthe present disclosure. The polysilicon stripe 906 is shown formed on anoxide layer 904 by a suitable deposition process, while the oxide layer904 is shown over a semiconductor substrate or body 902 comprised ofsilicon. The thickness 950 of the deposited polysilicon stripe 906 isnot necessarily larger than the diffusion depth of the dopants that maybe implanted subsequently, since a dopant specie which barely diffusesinto the oxide layer 904 is selected, e.g. such dopant atoms can bearsenic atoms, phosphorus atoms and etc.

FIG. 9B illustrates the polysilicon resistance temperature sensor 900after formation of mask 908 exposing a central portion of thepolysilicon stripe 906 in accordance with an aspect of the presentdisclosure. The resist mask 908 is shown having an opening 910. Theopening 910 is typically uniformly spaced along the polysilicon resistor906 so as to facilitate uniform dopant distribution of implanted dopantsin the longitudinal direction (y-direction) of the poly stripe 906. Thewidth 960 of the opening 910 can be varied. In one embodiment, the width960 is set to size X₁ to make sure the lateral diffusion range 964 ofthe subsequent implanted species in the lateral direction (x-direction)is within the region between two flanks 912 and 914 of the poly stripe906, or even has a significant distance away from the flanks. Then thefluctuations of the stripe width and thickness are eliminated fordetermining the absolute resistance value of the poly stripe, and thewidth 960 of mask opening 910 is now the critical dimension of the polystripe, while the masking technology has merely a 1%-2% error rangeimpact.

FIG. 9C illustrates the polysilicon resistance temperature sensor 900after ion implantation 916 in accordance with an aspect of the presentdisclosure. The ion implantation 916 implants a selected type ofdopants, which will not diffuse significantly into the oxide layer 904beneath the polysilicon stripe 906. Typical such dopants can be, e.g.arsenic atoms, or phosphorus atoms. The dopants pass through the opening910, but are resisted in other portions by the resist mask 908. As aresult, only a portion of the ions directed at the opening 910 areimplanted into the polysilicon resistor, forming an implanted region 906a. Subsequent to the implantation 916, the resist mask 908 is removed bya suitable process (e.g., chemical solution). Then, a thermal activationprocess is performed that diffuses the implanted dopant more uniformlythrough the polysilicon stripe 906, forming a diffused region 906 b.

Since the selected dopants cannot diffuse significantly into the oxidelayer 904, the diffused region 906 b may reach as far as the surface ofthe oxide layer 904, which leads to a reduction of the unwanted andundefined region 906 c. After the complete annealing of the implanteddopant, the introduced implantation dose and the masking 908 are thedetermine factors of the resistance value of the poly stripe, but notthe profile of the poly stripe.

FIGS. 10A, 10B and 10C depict a polysilicon resistance temperaturesensor 1000 being fabricated according to another aspect of the currentdisclosure. The device 1000 provided in FIG. 10 is different from thedevice 800 illustrated in FIG. 8 and the device 900 illustrated in FIG.9 in that the implanted dopant fulfills the polysilicon stripe 1006. Byneglecting the surface effects and by assuming the doping concentrationindependent from charge carrier mobility, the dopants may also fill theentire poly stripe, but without losing phonons mobility.

FIG. 10A depicts the polysilicon resistance temperature sensor afterformation of a polysilicon stripe 1006 in accordance with an aspect ofthe present disclosure. The polysilicon stripe 1006 is shown formed onan oxide layer 1004 by a suitable deposition process, while the oxidelayer 1004 is over a semiconductor substrate or body 1002 comprised ofsilicon. The thickness 1050 of the deposited polysilicon stripe 1006 isnot necessarily larger than the diffusion depth of the dopants implantedsubsequently, since a dopant species which barely diffuses into theoxide layer 904 is selected, e.g. the dopant atoms can be arsenic atoms,phosphorus atoms and etc.

FIG. 10B illustrates the polysilicon resistance temperature sensor 1000after formation of mask 1008 exposing a central portion of thepolysilicon stripe 1006 in accordance with an aspect of the presentdisclosure. The resist mask 1008 has an opening 1010. The opening 1010is typically uniformly spaced along the polysilicon resistor 1006 so asto facilitate uniform dopant distribution of implanted dopants in thelongitudinal direction (y-direction) of the poly stripe 1006. The width1060 of the opening 1010 can be varied. In one embodiment, the width1060 is set to size X₂ to make sure that the implanted dopant liescompletely within the polysilicon stripe 1006 and the diffused dopantsfill the entire poly stripe 1006.

FIG. 10C illustrates the polysilicon resistance temperature sensor 1000after ion implantation 1016 in accordance with an aspect of the presentdisclosure. The ion implantation 1016 implants a selected type ofdopants, which will not diffuse into the oxide layer 1004 below thepolysilicon stripe 1006. Typical such dopants can be, e.g. arsenicatoms, or phosphorus atoms. The dopants pass through the opening 1010,but are resisted in other portions by the resist mask 1008. As a result,only a portion of the ions directed at the opening 1010 are implantedinto the polysilicon stripe, forming an implanted region 1006 a.Subsequent to the ion implantation 1016, the resist mask 1008 is removedby a suitable process (e.g., chemical solution). Then, a thermalactivation process is performed that diffuses the implanted dopant moreuniformly through the entire polysilicon resistor 1006, forming adiffused region 1006 b which reaches the flanks 1012 and 1014 of thepoly stripe 1006.

Assuming that the doping concentration is approximately independent fromcharge carrier mobility, and by neglecting of surface effect, theresistance value in this approach is determined by the implantation doseand masking, but not by the structure of the poly stripe 1006, since theintegral of the conductivity over the cross section area 1006 isindependent from the distribution of the implanted dopant.

The above embodiments illustrated in FIGS. 8-10 have in common that theentire available dopants for current transportation are independent ofthe width and thickness of the poly stripe. The resistance is onlyaffected by the well-controllable processes of masking and ionimplantation. As a result, the width of the poly stripe can be reducedby a factor of 10. Since the poly stripe often has a length ofseveral-hundred micro-meters, the reduction of the width of the polystripe can save a significant surface area on the semiconductor device.

Further, the methods provided in the current disclosure is not limitedto produce polysilicon resistance temperature sensors, but can also beapplied to several applications of polysilicon resistors where highaccurate resistors are needed.

For the application of polysilicon resistors as temperature sensors, anexcellent temperature sensitivity of the polysilicon resistors isrequired, i.e. a strong temperature dependence of the resistors would bepreferred. For this purpose, in some embodiments, deep energy leveldonors are implanted into the poly resistors, so that the substancesinside the resistors contribute only a certain percentage to theconductivity at room temperature, but raise the conductivitysignificantly at higher temperature like e.g. 120° C. Typical such deepenergy level donors are selected from e.g. selenium, sulfur or nitrogen,etc. These deep energy level donors increase the efficient concentrationas temperature raises, which leads to a significant reduction of theresistivity of the resistor, or in other words, results an obviousincreasing of the conductivity of the resistor, therefore, a moretemperature-sensitive sensor is formed.

According to an aspect of the present disclosure, a method for producinga polysilicon resistor device is disclosed including: forming an undopedpolysilicon layer by deposition, and defining at least a portion thereofas a polysilicon resistor region; pre-implanting deep energy leveldonors into the polysilicon resistor region, so as to amorphize or atleast to partially amorphize the polysilicon resistor region; implantthe amorphized or partially amorphized polysilicon resistor region withsecond dopant atoms; and annealing at least the polysilicon resistorregion, so as to control the grain size in the polysilicon resistorregion.

According to a further aspect of the present disclosure, the methodfurther comprises forming an insulative layer beneath the polysiliconlayer, wherein the insulative layer is an oxide layer, and it is over asemiconductor substrate. According to one aspect of the presentdisclosure, the deposited polisilicon layer has a thickness in a rangeof between 200 nm and 400 nm.

According to a further aspect of the present disclosure, the methodfurther comprises forming contacts on ends of polysilicon resistorregion, defining a contact region. The contacts can be any kind ofconductivity contacts like, e.g. metal contacts. According to a furtheraspect of the present disclosure, deep energy level defects (or referredas deep level defects or deep defects) are formed by pre-implantation ofdeep level donors in the contact region, in order to reduce the Schottkybarrier in the contact region. Such deep energy level donors can be e.g.selenium, sulfur or nitrogen etc. Complementary or alternatively,shallow energy level atoms like phosphorus or arsenic atoms can beimplanted resulting in a surface concentration exceeding 1×10¹⁹ cm⁻³.According to a further aspect of the present disclosure, a mask (e.g., aresist mask) is formed exposing a pre-defined subarea of the polysiliconresistor region.

According to an aspect of the present disclosure, a method for producinga polysilicon resistor device is disclosed having: forming an undopedpolysilicon layer by deposition, and defining at least a portion thereofas a polysilicon resistor region; forming a mask (e.g., a resist mask)exposing a pre-defined subarea of the polysilicon resistor region;doping the polysilicon resistor region through the pre-defined subareawith dopant atoms; and creating diffusion of the dopant atoms, whereinthe dopant atoms diffuse at most within said polysilicon resistor regionof the polysilicon layer.

The pre-defined subarea may be a subarea in a central region of thepolysilicon resistor region. According to an aspect of the presentdisclosure, the dopant atoms can be e.g. phosphorous atoms. According toan alternative aspect of the present disclosure, the dopant atoms areselected from atoms that do not diffuse into other layers. Such dopantatoms comprise e.g. phosphorous atoms and arsenic atoms. According to afurther aspect of the present disclosure, the dopant atoms are selectedfrom deep energy level donors, so as to reduce the temperaturedependence of the resistivity of said polysilicon resistor region whenworking temperature increasing. Such deep energy level donors can bee.g. selenium, sulfur and nitrogen. According to a further aspect of thepresent disclosure, the dopant atoms are selected from deep energy levelacceptors.

The diffusion of dopant atoms may be created by annealing of at leastthe polysilicon resistor region.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present disclosure. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisdisclosure be limited only by the claims and the equivalents thereof.

What is claimed:
 1. A method for producing a polysilicon resistordevice, comprising: forming a polysilicon layer; forming an implantationmask over said polysilicon layer exposing a pre-defined subarea of saidpolysilicon layer; implanting dopant atoms into said pre-defined subareaof said polysilicon layer through said implantation mask; and creatingdiffusion of said dopant atoms, wherein said dopant atoms diffuse atmost within said polysilicon layer.
 2. The method of claim 1, whereinsaid dopant atoms diffuse at most within a portion of said polysiliconlayer.
 3. The method of claim 1, wherein forming said polysilicon layercomprises forming said polysilicon layer as an undoped layer.
 4. Themethod of claim 1, wherein forming said polysilicon layer is implementedby depositing polysilicon over an insulative layer.
 5. The method ofclaim 1, wherein the pre-defined subarea is a subarea in a centralregion of said polysilicon layer.
 6. The method of claim 1, wherein saiddopant atoms are selected from a group composed of phosphorous atoms andarsenic atoms.
 7. The method of claim 4, wherein the dopant atoms areselected from atoms that do not diffuse into said insulative layer. 8.The method of claim 2, wherein the diffusion of said dopant atoms iscreated by annealing of at least said portion of said polysilicon layer.9. The method of claim 1, wherein the dopant atoms comprise deep energylevel donors.
 10. The method of claim 9, wherein said deep energy leveldonors are selected from a group composed of selenium, sulfur andnitrogen.